Radio link monitoring in a wireless communication device for a enhanced control channel

ABSTRACT

A method ( 400 ) and user equipment ( 106 ) monitor a radio link for a wireless communication terminal for an enhanced control channel. A processor ( 304 ) may receive a first type of reference signal. The processor may monitor a first type of control channel. The processor may estimate a first synchronization condition associated with the radio link based on the first type of reference signal. The processor may monitor the second type of control channel. The processor may estimate a second synchronization condition associated with the radio link based on a second type of reference signal.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to the co-pending U.S. applicationSer. No. 13/428,479 filed concurrently herewith, the contents of whichare hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to wireless communications and moreparticularly to radio link monitoring in a wireless communicationterminal.

BACKGROUND

The Third Generation Partnership Project (3GPP) is developing a LongTerm Evolution (LTE) system using a physical layer based on globallyapplicable evolved universal terrestrial radio access (E-UTRA). A mobileterminal or station (MS), also referred to as User Equipment (UE), mayuse a measurement based on a cell-specific reference signal as a metricto determine if a radio link with the base station is in synchronizationor out of synchronization by determining whether reliable transmissionof a physical downlink control channel (PDCCH) codeword with specificdownlink message formats can be supported over the link.

In Release-8/9/10 of 3GPP, the UE Layer 1, such as or the physicallayer, monitors the downlink radio link quality of the serving cell,such as from a base station, for the purpose of indicating radio problemdetection status or radio link quality to higher layers. The radioproblem detection may be based on cell-specific reference signals. Innon-Discontinuous Reception (non-DRX) mode operations, such as when theUE is not in sleep mode, the UE in every radio frame checks the quality,measured over a time period, against thresholds (also known Qout andQin) defined implicitly by relevant requirements for detectingout-of-sync (OOS) and in-sync (IS) conditions, where the term “sync” issynchronization. For every radio frame, the UE indicates radio problemdetection to higher layers when the quality is worse than the thresholdQout and continues monitoring until either (a) the quality gets betterthan the threshold Qin, or (b) a radio link failure (RLF) is declared(after a certain timer expires) and the radio link recovery procedure isinitiated. Typically, a UE experiencing radio link quality issues withone serving cell (or enhanced Node B (eNB) or enhanced Base Station) maybe handed over to another serving cell (based on measurements providedby the UE to the eNB or network-aided measurements). However, for cases,e.g., where a UE in a connected state to a serving cell, but the UEsuddenly experiences severe sustained quality degradation and cannotreceive any messages from the serving cell, radio link failure occursand radio link recovery procedure is considered useful.

Typically the requirements are defined based on whether or not areference PDCCH Block Error Rate (BLER) is achieved for a particulardownlink control channel configuration. For example, for the Rel-8/9/10LTE, the OOS is reported to the higher layers from the lower layers if ahypothetical or reference PDCCH BLER becomes greater than 10% assumingthe transmission of a Downlink Control Information (DCI) Format 1A at aneight CCE aggregation level, which, for example, corresponds to a smallpayload size Downlink (DL) grant (used for scheduling data or broadcastcontrol transmissions) with the highest code protection (due to usingeight CCEs where eight is the maximum that can be assigned for a DCI).An IS condition is reported if the hypothetical or reference PDCCH BLERdrops below 2% assuming the transmission of a DCI Format 1C (with acertain different payload size) at a 4 CCE aggregation level, such asthe downlink control message associated with (for scheduling) thetransmission of a paging message or system information message (whichmay be typically broadcast information). In Rel-10 enhanced Inter CellInterference Coordination (eICIC), the base station (or eNB) can furtherconfigure the UE to monitor the radio link quality in only a subset ofsubframes. Based on the OOS and IS events, if it is determined that theradio link quality is poor, Radio Link Failure (RLF) may be declared.

In Rel-11, an enhanced control channel, such as an enhanced PDCCH(ePDCCH), may be specified for an ability to support increased controlchannel capacity, an ability to support frequency-domain ICIC, anability to achieve improved spatial reuse of control channel resource,an ability to support beamforming and/or diversity, and/or an ability tooperate on the new carrier type and in Multicast/Broadcast over a SingleFrequency Network (MBSFN) subframes.

If an enhanced control channel is specified, then there is a problemwith adapting Radio Link Monitoring (RLM). In particular, there is aneed for performing RLM at a UE on a Uu (eNB-UE) link when the eNB usesePDCCH as a control channel to communicate with the UE.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects, features and advantages of the disclosure willbecome more fully apparent to those having ordinary skill in the artupon careful consideration of the following Detailed Description thereofwith the accompanying drawings described below. The drawings may havebeen simplified for clarity and are not necessarily drawn to scale.

FIG. 1 is an example illustration of a communication system according toa possible embodiment;

FIG. 2 is an example illustration of a configuration of a computingsystem to act as a base station according to a possible embodiment;

FIG. 3 is an example illustration of a user equipment block diagramaccording to a possible embodiment;

FIG. 4 is an example illustration of a method for determining a radiolink quality of a radio link according to a possible embodiment;

FIG. 5 is an example illustration of a method for determining a radiolink quality of a radio link according to a possible embodiment;

FIG. 6 is an example illustration of a method for determining a radiolink quality of a radio link according to a possible embodiment;

FIG. 7 is an example illustration of a method for determining a radiolink quality of a radio link according to a possible embodiment;

FIG. 8 is an example illustration of a method for determining a radiolink quality of a radio link according to a possible embodiment; and

FIG. 9 is an example illustration of a time-frequency diagram of anexample subframe structure according to a possible embodiment.

DETAILED DESCRIPTION

A method and user equipment to monitor a radio link for a wirelesscommunication terminal when an enhanced control channel is configured isdisclosed. A transceiver may maintain a radio link with a network basestation. A processor may receive a first type of reference signal viathe transceiver. The processor may monitor, at the user equipment, afirst type of control channel, the first control channel demodulatedbased on a first type of reference signal. The processor may estimate afirst synchronization condition associated with the radio link based onthe first type of reference signal. The processor may acquireconfiguration information related to configuration of a second type ofcontrol channel, the second control channel demodulated based on asecond type of reference signal, the second reference signal distinctfrom the first type of reference signal received on the first carrier.The processor may monitor the second type of control channel. Theprocessor may estimate a second synchronization condition associatedwith the radio link based on a second type of reference signal. Theprocessor may send an output from a current layer to a higher layerbased on at least one of the estimated synchronization conditions.

FIG. 1 illustrates a communication system 100 including a network 102,base station, such as an eNB, 104 and user equipment (UE) 106. Variouscommunication devices may exchange data or information through thenetwork 102. The network 102 may be an evolved universal terrestrialradio access (E-UTRA) or other type of telecommunication network. Anetwork entity, such as the base station 104, may assign a UE identifier(UEID) to the UE 106 when the UE 106 first joins the network 102. Forone embodiment, the base station 104 may be a distributed set of serversin the network 102. The UE 106 may be one of several types of handheldor mobile devices, such as, a mobile phone, a laptop, or a personaldigital assistant (PDA). In one embodiment, the UE 106 may be a wirelesslocal area network capable device, a wireless wide area network capabledevice, or any other wireless device.

According to Release 8/9/10 of the E-UTRA or LTE standard, downlinkcommunications from an eNB to a UE utilizes orthogonal frequencydivision multiplexing (OFDM). In OFDM, orthogonal subcarriers aremodulated with a digital stream, which may include data, controlinformation, or other information, so as to form a set of OFDM symbols.The subcarriers may be contiguous or discontiguous and the downlink datamodulation may be performed using quadrature phase shift-keying (QPSK),16-ary quadrature amplitude modulation (16QAM), or 64QAM and typicallydownlink control modulation is QPSK. The OFDM symbols are configuredinto a downlink subframe (typically 1 millisecond duration) fortransmission from the base station. Each OFDM symbol has a time durationand is associated with a cyclic prefix (CP). A cyclic prefix is similarto a guard period between successive OFDM symbols in a subframe.Typically, the legacy Rel-8/9/10 control channel (PDCCH) is transmittedin the first few OFDM symbols at the beginning of the subframe and datais transmitted in the rest of the subframe.

The UE 106 may use an Enhanced Physical Downlink Control Channel(EPDCCH) to receive control information from the base station 104 (orfrom the network 102 in general). The EPDCCH may be Time DivisionMultiplexed (TDMed) with a Rel-8 PDCCH control channel and/or the EPDCCHmay be the only Downlink (DL) control channel carrying Downlink ControlInformation (DCI) in a subframe. The EPDCCH may be of Frequency DivisionMultiplexed (FDM) structure, such as by spanning all OrthogonalFrequency Division Multiplexed (OFDM) symbols of a subframe, as opposedto the Rel-8/9/10 PDCCH which spans only first 1˜4 OFDM symbols of thesub frame. Unlike the PDCCH, the EPDCCH can be accompanied by DedicatedReference Signals or Demodulation Reference Signals (DMRS), which can beused by the UE 106 to demodulate or decode the EPDCCH. The EPDCCH andthe associated DMRS can be transmitted in the same subframe. This can becontrast to PDCCH demodulation which is based on Cell-specific ReferenceSignals (CRS) where the CRS are transmitted in all DL sub frames and CRSmay be present in the subframes even if the UE is not receiving anyPDCCH. The EPDCCH may be sent in a set of Physical Resource Blocks(PRBs) which can be signaled via higher layer signaling or known to theUE 106 through other means. The UE monitoring of the control channelsmay be of various types including the following:

1. UE monitors only PDCCH in a DL subframe (i.e., similar toRel-8/9/10);

2. UE monitors only EPDCCH in a DL subframe;

3. UE monitors both PDCCH and EPDCCH in a DL subframe (the total numberof blind decodes are split between PDCCH and EPDCCH monitoring);

-   -   a. UE monitors CSS (Common Search Space, typically to look for        broadcast control messages such as paging, System Information        (SI), Random Access (RA) response, etc.) for PDCCH and UESS        (UE-Specific Search Space) for EPDCCH;    -   b. UE monitors CSS and some UESS for PDCCH and UESS for EPDCCH;    -   c. UE monitors UESS for PDCCH and CSS for EPDCCH;    -   d. UE monitors CSS for PDCCH and CSS for EPDCCH and UESS for        PDCCH and UESS for EPDCCH; and/or

e. UE monitors CSS and UESS for EPDCCH in a first set of subframes andmonitors CSS and UESS for PDCCH in a second set of subframes, where thefirst and second set of subframe may or may not overlap.

It is noted that the CSS in the PDCCH and CSS in the EPDCCH may bedistinct, i.e., have different characteristics, such as differenttime-frequency locations, different RS for demodulation, etc. Thus, insome instances, the CSS in the EPDCCH may also be referred to as anenhanced Common Search Space (or eCSS) for distinction. Similarly, it isnoted that the UESS in the PDCCH and UESS in the EPDCCH may be distinct,i.e., have different characteristics such as different time-frequencylocations, different RS for demodulation, etc. Thus, in some instances,the UESS in the EPDCCH may also be referred to as an enhancedUE-specific Search Space (or eUESS) for distinction. Other search spacessuch as carrier-specific search space, virtual cell-specific searchspace, etc may also be defined.

FIG. 2 illustrates a possible configuration of a computing system to actas a base station 104. The base station 104 may include aprocessor/controller 210, a memory 220, a database interface 230, atransceiver 240, input/output (I/O) device interface 250, and a networkinterface 260, connected through bus 270. The base station 104 mayimplement any operating system, such as Microsoft Windows®, UNIX, orLINUX, for example. Client and server software may be written in anyprogramming language, such as C, C++, Java or Visual Basic, for example.The server software may run on an application framework, such as, forexample, a Java® server or .NET® framework.

The processor/processor 210 may be any programmable processor. Thesubject of the disclosure may also be implemented on a general-purposeor a special purpose computer, a programmed microprocessor ormicroprocessor, peripheral integrated circuit elements, anapplication-specific integrated circuit or other integrated circuits,hardware/electronic logic circuits, such as a discrete element circuit,a programmable logic device, such as a programmable logic array, fieldprogrammable gate-array, or the like. In general, any device or devicescapable of implementing the decision support method as described hereinmay be used to implement the decision support system functions of thisdisclosure.

The memory 220 may include volatile and nonvolatile data storage,including one or more electrical, magnetic or optical memories such as arandom access memory (RAM), cache, hard drive, or other memory device.The memory may have a cache to speed access to specific data. The memory220 may also be connected to a compact disc-read only memory (CD-ROM),digital video disc-read only memory (DVD-ROM), DVD read write input,tape drive, or other removable memory device that allows media contentto be directly uploaded into the system. Data may be stored in thememory 220 or in a separate database. The database interface 230 may beused by the processor/controller 210 to access the database. Thedatabase may contain any formatting data to connect the UE 106 to thenetwork 102. The transceiver 240 may create a data connection with theUE 106. The transceiver may configure a Physical Downlink ControlChannel (PDCCH) and a Physical Uplink Control Channel (PUCCH) betweenthe base station 104 and the UE 106.

The I/O device interface 250 may be connected to one or more inputdevices that may include a keyboard, mouse, pen-operated touch screen ormonitor, voice-recognition device, or any other device that acceptsinput. The I/O device interface 250 may also be connected to one or moreoutput devices, such as a monitor, printer, disk drive, speakers, or anyother device provided to output data. The I/O device interface 250 mayreceive a data task or connection criteria from a network administrator.

The network connection interface 260 may be connected to a communicationdevice, modem, network interface card, a transceiver, or any otherdevice capable of transmitting and receiving signals from the network106. The network connection interface 260 may be used to connect aclient device to a network. The network connection interface 260 may beused to connect the teleconference device to the network connecting theuser to other users in the teleconference. The components of the basestation 104 may be connected via an electrical bus 270, for example, orlinked wirelessly.

Client software and databases may be accessed by the processor/processor210 from memory 220, and may include, for example, databaseapplications, word processing applications, as well as components thatembody the decision support functionality of the present disclosure. Thebase station 104 may implement any operating system, such as MicrosoftWindows®, LINUX, or UNIX, for example. Client and server software may bewritten in any programming language, such as C, C++, Java or VisualBasic, for example. Although not required, the disclosure is described,at least in part, in the general context of computer-executableinstructions, such as program modules, being executed by the electronicdevice, such as a general purpose computer. Generally, program modulesinclude routine programs, objects, components, data structures, etc.that perform particular tasks or implement particular abstract datatypes. Moreover, those skilled in the art will appreciate that otherembodiments of the disclosure may be practiced in network computingenvironments with many types of computer system configurations,including personal computers, hand-held devices, multi-processorsystems, microprocessor-based or programmable consumer electronics,network PCs, minicomputers, mainframe computers, and the like.

FIG. 3 illustrates in a block diagram one embodiment of atelecommunication apparatus or electronic device to act as the UE 106.The UE 106 may be capable of accessing the information or data stored inthe network 102. For some embodiments of the disclosure, the UE 106 mayalso support one or more applications for performing variouscommunications with the network 102. The UE 106 may be a handhelddevice, such as, a mobile phone, a laptop, or a personal digitalassistant (PDA). For some embodiments, the UE 106 may be WiFi® capabledevice, which may be used to access the network 102 for data or by voiceusing VOIP.

The UE 106 may include a transceiver 302, which is capable of sendingand receiving data over the network 102. The UE 106 may include aprocessor 304 that executes stored programs. The UE 106 may also includea volatile memory 306 and a non-volatile memory 308 which are used bythe processor 304. The UE 106 may include a user input interface 310that may comprise elements such as a keypad, display, touch screen, andthe like. The UE 106 may also include a user output device that maycomprise a display screen and an audio interface 312 that may compriseelements such as a microphone, earphone, and speaker. The UE 106 alsomay include a component interface 314 to which additional elements maybe attached, for example, a universal serial bus (USB) interface.Finally, the UE 106 may include a power supply 316.

In operation, the processor 304 can receive a first type of referencesignal. The processor 304 can monitor a first type of control channel,such as a Physical Downlink Control Channel (PDCCH). The first controlchannel can be demodulated based on the first type of reference signal,such as a Cell-specific Reference Signal (CRS). The processor 304 canestimate a first synchronization condition, such as anout-of-synchronization (OOS) or an in-synchronization (IS) condition,associated with the radio link based on the first type of referencesignal.

The processor 304 can acquire configuration information related toconfiguration of a second type of control channel, such as an EnhancedPhysical Downlink Control Channel (EPDCCH) received on the firstcarrier. The second control channel can be demodulated based on a secondtype of reference signal. The processor 304 can receive the second typeof reference signal. The second reference signal can be distinct fromthe first type of reference signal. For example, the second type ofreference signal can be a Channel State Information Reference Signal(CSI-RS) or a Demodulation Reference Signal (DMRS). The first type ofreference signal and the second type of reference signal may be receivedon the same carrier. Alternatively, the first type of reference signalmay be received on a first carrier and the second type of referencesignal may be received on a second carrier, where the second carrier canbe distinct from the first carrier. Also the first type of referencesignal may be received in a first set of subframes and the second typeof reference signal may be received in a second set of subframes. Thefirst and second set of subframes may overlap or may not overlap.

The processor 304 can monitor the second type of control channel. Theprocessor 304 can estimate a second synchronization condition (OOS)associated with the radio link based on a second type of referencesignal. The processor 304 can send an output from a current layer to ahigher layer based on at least one of the estimated synchronizationconditions. The processor 304 can send an indicator to a base stationbased on the output sent to the higher layer.

According to a related embodiment, the processor 304 can acquiresignaling, such as an EPDCCH configuration signal, configuring the userequipment 106 to monitor a first type of control channel (EPDCCH). Thefirst type of control channel demodulated based on a first type ofreference signal (DMRS).

The processor 304 can receive a second type of reference signal, such asa CSI-RS, in at least one or more sets of resource blocks or a resourceblock set. The processor 304 can estimate a synchronization conditionbased on the received second type of reference signal, such as theCSI-RS, and at least one attribute of the control channel. The processor304 can also estimate the synchronization condition based on thereceived second type of reference signal, such as a CSI-RS, and thefirst type of reference signal, such as a DMRS. The processor 304 cansend an output from a current layer to a higher layer in the UE 106based on the estimated synchronization condition.

The processor 304 can estimate the synchronization condition based onthe received second type of reference signal, such as a CSI-RS, and atleast one attribute of the first type of control channel, such as anattribute of EPDCCH. The processor 304 can estimate the synchronizationcondition based on a third type of reference signal (CRS) and at leastone attribute of a second type of control channel (PDCCH).

The processor 304 can also estimate a synchronization condition bydetermining a channel state based on the received second type ofreference signal wherein the second type of reference signal is receivedon an antenna port and by ascertaining the synchronization conditionbased on the channel state. The processor 304 can acquire signaling toconfigure the user equipment to monitor a search space used by thecontrol channel.

The first type of reference signal can be the same as the third type ofreference signal. The second type of reference signal can be the same asthe third type of reference signal. The first type of reference signalcan also be distinct from the second type of reference signal.

The processor 304 can detect a synchronization condition by estimating achannel state based on the second type of reference signal. Theprocessor 304 can estimate a Block Error Rate (BLER) corresponding to areference scheduling grant. For example, the reference scheduling grantcan be downlink or uplink, can have a DCI Format size, and/or can havean associated Search space. The processor 304 can compare the blockerror rate to a threshold to detect a synchronization condition.

According to a related embodiment, the UE 106 can use a different methodfor OOS/IS condition based on the type of control channel the UE 106 ismonitoring. For example, when the UE 106 monitors the PDCCH, it can usethe PDCCH reference (1A with 8 CCE for OOS condition and 1C with 4CCEfor IS condition) and Cell-specific Reference Signal (CRS) for RadioLink Monitoring (RLM), and when the UE 106 is configured to monitor theEPDCCH, it can use the EPDCCH reference (1A with 8 eCCE for OOS and 1Cwith 4 eCCE for IS) and a second reference signal (DMRS or CSI-RS) forRLM. The configuration of the resources used for EPDCCH can be done viahigher-layer signaling. A hybrid scheme is also possible. For example,if the UE 106 is configured to monitor CSS for PDCCH and UESS forEPDCCH, the OOS may be based on the legacy control channel (PDCCH), suchas 1C with 4CCE, and the IS may be based on EPDCCH (1A with 8 eCCE) andvice-versa. In another example, the UE 106 can be configured to monitorUESS and CSS for PDCCH in a first set of subframes (or a subframesubset) where the PDCCH can be demodulated using a third type ofreference symbol (e.g. CRS) and can be configured to monitor UESS andCSS for EPDCCH in a second set of subframes (or a subframe subset) wherethe EPDCCH can be demodulated using a first type of reference symbol(e.g. DMRS). In this example, the OSS and IS may be based on anycombination of UE 106 monitoring with a PDCCH reference with the thirdtype of reference symbol (which may only occur in the first set ofsubframes (or a subframe subset)) and/or UE 106 monitoring with a EPDCCHreference using a first and/or second type of reference symbol (DMRSand/or CSI-RS) for RLM (where the EPDCCH may only occur in the secondset of subframes (or a subframe subset)).

Further operations of the UE 106 are described in the methods below.

FIG. 4 is an example illustration of a method 400 for determining aradio link quality of a radio link by the UE 106 according to a possibleembodiment. At 415, the UE 106 can receive a first type of referencesignal.

At 420, the UE 106 can monitor a first type of control channel, thefirst type of control channel demodulated based on the first type ofreference signal. The UE 106 can monitor the first type of controlchannel by monitoring a first common search space associated with thefirst type of control channel. At 425, the UE 106 can estimate a firstsynchronization condition (OOS) associated with the radio link based onthe first type of reference signal. The first type of control channelmonitored can span the entire first carrier bandwidth and the secondtype of control channel monitored can span only a portion of the firstcarrier bandwidth. The UE 106 can assume that the first type of controlchannel monitored can span the bandwidth of a first carrier used fortransmitting the first type of control channel. The UE 106 can alsoassume that the second type of control channel monitored spans only aportion of the bandwidth of a second carrier used for transmitting thesecond type of control channel.

At 430, the UE 106 can acquire configuration information related toconfiguration of a second type of control channel, such as an EPDCCH.The second type of control channel can be demodulated based on a secondtype of reference signal. The second reference signal can be distinctfrom the first type of reference signal, such as a CSI-RS or a DMRS.

At 435, the UE 106 can monitor the second type of control channel. TheUE 106 can monitor the second type of control channel by monitoring asecond common search space associated with the second type of controlchannel. It is noted here that the UE can monitor a control channel mayalso imply that the UE can monitor for the control channel. This coversthe case where the UE is looking for, but may not receive valid DCI,e.g. is some subframes or in DRX period. It can be understood that themonitoring step implies the UE performing an attempt to detect a controlchannel. Similarly, instead of a subset of subframes, a subframe subsetcan be used. Similarly, instead of a set of resource blocks, a resourceblock set can be used.

At 440, the UE 106 can estimate a second synchronization condition, suchas out-of-sync (OOS) associated with the radio link based on the secondtype of reference signal. The second synchronization condition can beestimated based on at least one of a set of configured Virtual ResourceBlocks (VRBs) (virtual resource block set) or a set of configuredsubframes (or a subframe subset). The second synchronization conditioncan be estimated based on antenna port set configuration for EPDCCHtransmission. For example, an EPDCCH configuration message can indicatethat a DMRS antenna port 7 is used or that a DMRS antenna port set{8,10} with rank 2 transmission (or transmit diversity scheme) is used.The second synchronization condition can also be estimated based onEnergy Per Resource Element (EPRE) information relating to EPDCCHtransmission. For example, the EPDCCH configuration message can includethe range of EPDCCH power boosts that the eNB intends to use relative tofor example, CRS or CSI-RS, such as by signaling a ratio of the EPDCCHEPRE to CRS EPRE or a EPDCCH EPRE to CSI-RS EPRE (or to any otherreference signal) for EPDCCH. The second synchronization condition canalso be estimated based on assuming at least one of a hypothetical or areference downlink assignment or an uplink grant. Further assumptionsfor estimating the second synchronization condition can be acquired viaconfiguration signaling or higher layer signaling. For example, theassumptions for the second synchronization condition can includeenhanced Control Channel Element (CCE) size, enhanced CCE aggregationlevel, and other assumptions. The second synchronization condition (OOS)associated with the radio link that is further based on the first typeof reference signal can be further estimated. As an example, anout-of-synchronization condition of the radio link can be determined ifthe first synchronization condition is out-of-synchronization and thesecond synchronization condition is out-of-synchronization.

At 445, the UE 106 can send an output from a current layer to a higherlayer based on at least one of the estimated synchronization conditions.For example, the output can signal the UE 106 to stop receiving secondcontrol channel or to switch control channels. Sending the output canalso include sending an estimated condition, can include sending anchannel quality indicator, can include sending information regarding thesynchronization condition, or can include sending any other output basedon an estimated condition. The UE 106 can send an output by sending anindicator to a base station via the transceiver 302 based on the outputsent to the higher layer. Both layers are may be inside the processor304 and the UE can also send an output from one layer inside theprocessor 304 to another layer inside the processor 304.

The first type of control channel can be a Physical Downlink ControlChannel (PDCCH) and the second type of control channel can be anenhanced Physical Downlink Control Channel (EPDCCH). The first type ofreference signal can be a Cell-specific Reference Signal (CRS) and thesecond reference signal can be a Demodulation Reference Signal (DMRS) ora Channel State Information Reference signal (CSI-RS).

A synchronization condition can be an out-of-synchronization condition(OOS) or an in-synchronization (IS) condition. For example, the firstsynchronization condition can be an out-of-synchronization condition andthe second synchronization condition can be an in-synchronizationcondition. As a further example, indications of these conditions can beused by a higher layer such as the radio resource control layer or Layer3 to trigger a radio link monitoring procedure. According to oneexample, if Layer 3 receives, a number of OOS indications, such as basedon a N311 counter, a T310 timer can be started. If no IS indications arereceived before T310 expires, the Layer 3 can declare a Radio LinkFailure and can suspend uplink transmissions. As an alternate example,if Layer 3 receives a number of IS indications, such as based on a N313counter, before T310 expires, the Layer 3 can declare a Radio LinkRecovery and the UE 106 can resume normal operation. The value of thetimers and counters may vary based on the RLM technique being used inthe UE. At 450, the method 400 can end.

FIG. 5 is an example illustration of a method 500 for determining aradio link quality of a radio link by the UE 106 according to a possibleembodiment. At 510, the method begins. At 515, a UE 106 can acquiresignaling, such as an Enhanced Physical Downlink Control Channel(EPDCCH) configuration signal. For example, the processor 304 canacquire signaling based on which the user equipment monitors for a firsttype of control channel, where the first type of control channel can bedemodulated based on a first type of reference signal. The signaling canidentify one of a configured set of Resource Blocks (RBs) or resourceblock set. The signaling can also identify at least one antenna portassociated with the control channel. For example, DMRS for EPDCCH canuse antenna ports 7-10. The signaling can also identify at least oneconfigured subframe subset containing a second type of reference signal.The signaling can configure the UE 106 to monitor a first type ofcontrol channel, such as an EPDCCH. The first type of control channelcan be demodulated based on a first type of reference signal, such as aDemodulation Reference Signal (DMRS).

At 520, the UE 106 can receive the second type of reference signal, suchas a Channel State Information Reference Signal (CSI-RS), in at leastone or more sets of resource blocks (or resource block set). Theresource blocks may be resource blocks or virtual resource blocks. Thevirtual resource blocks can be localized virtual resource blocks, suchas a set of contiguous RBs, or distributed virtual resource blocks, suchas a set of non-contiguous RBs distributed across the downlinktransmission bandwidth. The second type of reference signal can bedistinct from the first type of reference signal. For example, thesecond type of reference signal can be a CSI-RS and the first type ofreference signal can be a DMRS.

As a further example, higher layer signaling can be received, where thehigher layer signaling can configure the UE 106 to monitor a searchspace used by a control channel where the control channel can bedemodulated based on a demodulation reference signal (DMRS). A DMRStransmission can be received over a set of resource blocks. Then, asynchronization condition can be determined based on the DMRS and higherlayer signaling. As another example of DMRS, the DMRS for EPDCCH can useantenna ports 7-10. The higher-layer signaling can includes a set ofsubframes over which the first type of reference signal, such as a DMRS,is received. As a further example, an eNB 104 can configure transmissionof DMRS with some pre-determined periodicity.

At 525, the UE 106 can estimate a synchronization condition based on thereceived second type of reference signal and based on at least oneattribute of the control channel. The attribute of the control channelcan be received from the EPDCCH configuration signaling, can be separatesignaling, can be set according to a specification, such as 1A/6 eCCE,1C/5 eCCE, or other enhanced Control Channel Elements (CCE), or it canbe otherwise determined. Since the eCCE size may be variable based onthe subframe configuration, a reference eCCE size used for estimation ofthe synchronization may be signaled by the eNB either implicitly orexplicitly or may be derived by the UE implicitly or explicitly. In oneexample, an eCCE size may vary from 18 Resource Elements to 144 ResourceElements and in another example, an eCCE size may be defined as thenumber of resource elements available for an ePDCCH in one ResourceBlock pair. The UE 106 can estimate a synchronization condition based onthe received second type of reference signal, such as CSI-RS and basedon the first type of reference signal, such as DMRS.

The UE 106 can estimate a synchronization condition based on thereceived second type of reference signal, such as the CSI-RS, and atleast one attribute of the first type of control channel, such as theEPDCCH and also based on a third type of reference signal, such as aCell-specific Reference Signal (CRS), and at least one attribute of asecond type of control channel, such as a legacy Physical DownlinkControl Channel (PDCCH). The synchronization condition can be anout-of-synchronization condition or an in-synchronization condition. Theat least one attribute of the control channel can be a referenceenhanced control channel element (eCCE) size, can be a referenceaggregation level for aggregation of eCCEs, can be a localized or adistributed transmission of the eCCEs, can be a reference transmissionscheme associated with the control channel or the eCCE, can be areference search space associated with the control channel, or can beany other attribute.

At 530, the UE 106 can send an output from a current layer to a higherlayer in the UE 106 based on the estimated synchronization condition.For example, the UE 106 can send an output from a physical layer or aLayer 1 to a higher layer in the UE 106. Both layers are may be insidethe processor 304 and the UE can send an output from one layer insidethe processor 304 to another layer inside the processor 304.

According to a related embodiment, at 515, the UE can acquire signalingto configure the UE 106 to monitor a search space used by the controlchannel. At 525, the UE 106 can estimate a synchronization conditionbased on the received second type of reference signal, such as a CSI-RS,and at least one attribute of the control channel by determining achannel state based on the received second type of reference signalwhere the second type of reference signal is received on an antenna portand by ascertaining the synchronization condition based on the channelstate. The UE 106 can determine the channel state based on asignal-to-noise ratio (SNR) gain parameter, where the signal-to-noiseratio gain parameter can be acquired via signaling. The signaling can behigher than physical layer signaling, or the parameter can be in EPDCCHconfiguration signaling. Alternatively, the SNR gain parameters (ortransmit beam forming weights) acquired from higher layer signaling canbe used in connected non-DRX mode and a pre-determined constant SNR gain(such as SNR gain of 0 dB) can be assumed for DRX mode. The UE 106 candetermine the channel state based on a transmission scheme, wheretransmission scheme information can be acquired via signaling. Again,the signaling can be higher than physical layer signaling, ortransmission scheme information can be in the EPDCCH configurationsignaling.

The higher-layer signaling can include a set of resource blocks (orresource block set) over which synchronization detection can beperformed. The higher-layer signaling can also include an antenna portindex associated with the first type of reference channel over whichsynchronization detection must be performed. At 530, the method 500 canend.

FIG. 6 is an example illustration of a method 600 for determining aradio link quality of a radio link by the UE 106 according to a possibleembodiment. Elements of the method 600 can be combined with elements ofthe method 500. At 610, the method begins. At 615, the UE can receive anenhanced control channel codeword, such as an EPDCCH codeword, on a sameset of resource blocks as the first type of reference signal, such as ademodulation reference signal. At 620, the UE can decode the enhancedcontrol channel codeword. At 625, the UE can compare an estimated BlockError Rate (BLER) to a threshold to detect the synchronizationcondition. The BLER may correspond to a hypothetical EPDCCH transmissionsuch as DCI 1A (i.e. for a reference payload size) with 8 eCCE (e.g.corresponding to a reference coding rate and/or modulation and/ortransmission scheme). At 630, the method 600 can end.

FIG. 7 is an example illustration of a method 700 for determining aradio link quality of a radio link according to a possible embodiment.Elements of the method 700 can be combined with elements of the othermethods above. At 710, the method begins. At 715, the UE 106 can detecta synchronization condition by estimating a channel state based on thesecond type of reference signal. At 720, the UE 106 can estimate a BlockError Rate (BLER) corresponding to a reference scheduling grant. Thereference scheduling grant can be a downlink scheduling grant, can be anuplink scheduling grant, can have a Downlink Control Information (DCI)format size, and/or can have an associated search space. At 725, the UE106 can compare the block error rate to a threshold to detect asynchronization condition. At 730, the method can end.

FIG. 8 is an example illustration of a method 800 for determining aradio link quality of a radio link according to a possible embodiment.Elements of the method 700 can be combined with elements of the othermethods above. At 810, the method can begin. At 815, the UE 106 candetect a synchronization condition by receiving an enhanced controlchannel codeword on a subset of resource blocks. For example the UE 106can perform a cyclic redundancy check (CRC) check on EPDCCH. At 820, theUE 106 can decode the codeword. For example, the UE 106 can determinewhether the CRC passed or failed. At 825, the UE 106 can estimate aBlock Error Rate (BLER) based on the decoding. At 830, the UE 106 cancompare the estimated BLER to a threshold to detect the synchronizationcondition, such as an out-of-sync or in-sync condition. At 835, themethod can end.

Embodiments can detect out-of-sync and in-sync conditions based on CRSand DMRS. A UE can use a different method for OOS/IS condition based onthe type of control channel the UE is monitoring. For example, when theUE monitors the PDCCH, it can use a PDCCH reference, such DCI Format 1Awith 8 CCE and Format 1C with 4CCE and CRS for RLM. When the UE isconfigured to monitor the EPDCCH, it can use DCI Format 1A with 8enhanced CCE (eCCE) and DCI Format 1C with 4 eCCE and a second referencesignal, such as DMRS or CSI-RS for RLM. The configuration of theresources used for EPDCCH can be done via higher-layer signaling. Arelated embodiment can use a hybrid scheme where the UE can beconfigured to monitor Common Search Space (CSS) in PDCCH and UE-SpecificSearch Space (UESS) in EPDCCH. The OOS may be based on EPDCCH, such as1A with 8eCCE and the IS can be based on legacy indication, such asFormat 1C with 4 CCE, and vice-versa.

According to some embodiments, a UE can use DMRS for EPDCCHdemodulation, but the DMRS may not be present in every subframe. Thus,the UE can use the CSI-RS to determine the channel condition and usethat to detect OOS/IS events. According to some embodiments, an eNB canconfigure periodic CSI-RS schedule, such as 1 subframe out of 40subframes, the eNB can transmit CSI-RS according to this schedule, andthe UE uses the CSI-RS and the configuration information to detectOOS/IS events. According to some embodiments, the eNB can configureperiodic DMRS schedule, such as 1 subframe out of 40 subframes, the eNBcan transmit DMRS according to this schedule where precoding to generateDMRS in these subframes can be identical to what is used for EPDCCHtransmission, and the UE can use this information to detect OOS/ISevents.

For behavior upon RLF detection, the Rel-8 UE procedure for RLM does notinvolve network signaling (i.e., UE RLF is deduced by the network bysuspension of UE UL transmission after the expiry a timer). But, withEPDCCH on the other hand, UE sending an indication that an RLF hasoccurred can lead to measures for improving the EPDCCH link by the eNBsuch as to re-configuration of EPDCCH configuration such as changing ofantenna precoding coefficients associated with DMRS ports, EPDCCH powerboosting, changing of the set of RBs configured for EPDCCH, etc.Therefore, UE can indicate that an RLF has occurred (or near occurrence)to the eNB. The UE can suspend UL until T310 expires and then attemptRRC connection re-establishment if the EPDCCH is not configured beforethe timer expires. The ACK/NACK PUCCH resources available to the UE totransmit uplink signals can be configured via higher layer signaling.Thus, if such resources are available, the UE may use those resourcesfor sending an indication to the eNB that an RLF has occurred.

For taking minimum across block error rates, the UE may use both theEPDCCH and the PDCCH to maintain the radio link. In that case, the UEmay detect (or trigger) an event only if the quality on both the EPDCCHand PDCCH deteriorate, e.g. a UE may declare an OOS event only if thePDCCH BLER estimate falls below a threshold and the EPDCCH BLER estimatefalls below the same or a different threshold.

For OOS detection, the UE can receive a first type of reference signal,such as CRS, and a second type of reference signal such as DMRS. The UEcan compute BLER for both possibilities, CRS and DMRS and send anout-of-sync indication if min(BLER_(PDCCH), BLER_(EPDCCH)) exceeds aQout threshold (say, min(BLER_(CRS), BLER_(DMRS))>10%), where BLER_(CRS)is BLER corresponding to hypothetical DCI 1A 8CCE transmission assumingCRS demodulation and BLER_(DMRS) is BLER corresponding to hypotheticalDCI 1A with 6eCCE transmission assuming DMRS demodulation.

For IS detection, the UE can receive a first type of reference signalsuch as CRS and a second type of reference signal such as DMRS. The UEcan compute BLER for both possibilities, CRS and DMRS and send in-syncindication if min(BLER_(PDSCCH), BLER_(EPDCCH)) falls below a Qinthreshold (say, min(BLER_(CRS), BLER_(DMRS))<2%), where BLER_(CRS) canbe BLER computed for hypothetical DCI 1C 4CCE transmission assuming CRSdemodulation and BLER_(DMRS) is BLER computed for hypothetical DCI 1C2eCCE transmission assuming DMRS demodulation.

FIG. 9 is an example illustration of a time-frequency diagram 900 of anexample subframe structure according to a possible embodiment. Thetime-frequency diagram 900 of the subframe structure can depict exampledistributions of reference signals, and particularly Common ReferenceSignals (CRS) and UE specific reference signals (UERS) or Demodulationreference signals (DMRS), in a OFDMA subframe that may be employed bycommunication system 100 in accordance with various embodiments of thepresent disclosure. A vertical scale of time-frequency diagram 900depicts multiple blocks of frequency, or frequency bins, (frequencysubcarriers) of the subframe that may be allocated. A horizontal scaleof time-frequency diagram 900 depicts multiple blocks of time (in unitsof OFDM symbols) of the subframe that may be allocated. A subframecomprises multiple resource blocks (RBs) such as Resource Block 0 (RB0),Resource Block 1 (RB1), Resource Block 2 (RB2), and Resource Block 3(RB3), wherein each RB comprises 12 OFDM subcarriers over a time slotcomprising seven (7) OFDM symbols for the normal CP case. Typically, thesubframe duration is 1 ms and it can comprise two time slots of 0.5 msduration each. In turn, each RB can be divided into multiple resourceelements (REs), wherein each RE is a single OFDM subcarrier, orfrequency bin, on a single OFDM symbol.

For LTE Release 11, a UE such as UE 106 can receive the EPDCCH in a setof RBs that may span only a portion of the carrier bandwidth infrequency domain. As depicted in a subframe in time-frequency diagram,the UE 106 may expect to receive the EPDCCH and the PDSCH, wherein theEPDCCH can be sent to the UE in RB0 and RB1 the PDSCH is sent to the UEin RB2 and RB3. In order to decode the information sent on the PDCCH,the UE 106 can perform channel estimation after receiving the PDCCH. Toperform channel estimation, the UE 106 can receive Reference Signals(RSs) that can be included in the subframe. The RSs can be associatedwith one or more antenna ports. For example, RSs labeled R0 can beresource elements carrying reference signals associated with antennaport 0, RSs labeled R1 can be resource elements carrying referencesignals associated with antenna port 1, RSs labeled R2 can be resourceelements (REs) carrying reference signals associated with antenna port2, and RSs labeled R3 can be resource elements (REs) carrying referencesignals associated with antenna port 3. The RSs associated with antennaports 0, 1, 2, and 3, can also be known as “Cell-specific ReferenceSignals (CRS).” In order to demodulate user data (sent on PDSCH), 3GPPLTE Release 10 provides that a UE, such as UE 106, can either use theRSs associated with antenna ports 0, 1, 2, and 3 or can use RSsassociated with other antenna ports, such as antenna ports 7, 8, 9, 10,11, 12, 13, and 14, that is, the UE can use RSs associated with all or asubset of these antenna ports, based on the transmission scheme used forPDSCH reception (in turn, the transmission scheme depends onconfiguration signaling from the eNB). The RSs associated with theseother antenna ports 7, 8, 9, 10, 11, 12, 13, and 14 are typicallyreferred to as “UE specific reference signals (UERS)” or “Demodulationreference signals (DMRS) or Dedicated reference signals (DRS).” Unlikethe PDCCH, which is received by the UE using CRS, the EPDCCH is receivedby the UE using DMRS.

REs labeled R0-R3 (and associated with antenna ports 0-3, respectively)can be allocated to CRS (CRS REs) and REs labeled R7-R10 (and associatedwith antenna ports 7-10, respectively) are allocated to DMRS (DMRS REs).Typically, RSs corresponding to antenna ports 7 and 8 are multiplexedusing CDM (or other scheme) and are mapped to the same REs in time andfrequency domain. The subframe can also include other RSs that aredistributed in the control regions and/or user data regions of thesubframe. These other RSs may be present but are not necessarily usedfor demodulation of received signals by a UE in an LTE-A communicationsystem. For example, the other RS may include the CSI-RS (Channel StateInformation reference signal) or muted RS where the UE can assume andzero transmission power on the RS Res that may be useful forinterference measurements, or may include positioning RS that may beused for detecting location information, etc. The CSI-RS is typicallynot used for demodulation purposes and may be present in occasionalsubframes, i.e. the subframe periodicity and the number of CSI-RSantenna ports are configurable via higher layer signaling. CSI-RStypically occupy REs that are not occupied by CRS, potential DMRS, etc.

Further, RSs corresponding to an antenna port can be allocated to aresource element (RE) pair in user data regions, and more particularlyto one of the RE pairs associated with OFDM symbols. For example, pairsof adjacent DMRS RE labeled as R7/8 may be allocated to antenna port 7and antenna port 8 and, pairs of adjacent DMRS RE labeled as R9/10 maybe allocated to antenna port 9 and antenna port 10. In this example, theRS for R7 and R8 can be code-division multiplexed using orthogonal Walshcodes. Similarly, the RS for R9 and R10 can be code-division multiplexedusing orthogonal Walsh codes.

The UE 106 can monitor EPDCCH in a set of RBs (EPDCCH RB set) that mayspan only a portion of the carrier bandwidth in frequency domain.Further, the UE 106 may monitor the EPDCCH in only those time symbols inthe subframe that are distinct from the time symbols corresponding toPDCCH. For example, the UE 106 can monitor PDCCH across the entirecarrier bandwidth in frequency domain and in time symbols in the timedomain (i.e., there are two control symbols in the example). The UE 106can monitor EPDCCH in one (e.g. RB0) or more RBs (i.e. RB0 and RB1) infrequency domain and symbols or alternately, symbols in the time domain.For example, considering RB0, the UE 106 can monitor EPDCCH in thatportion of RB0 that is not allocated for PDCCH. Alternately, RB0 may bedefined to cover only the non-PDCCH control region resources i.e.excluding the resources assigned for PDCCH. In an alternate embodiment,RB0 may be defined to start from a pre-determined symbol and occupy theremaining symbols in the slot. The pre-determined symbol may be signaledto the UE via PDCCH or higher layer signalling (e.g., RRC or MACsignalling). To receive the EPDCCH, the UE 106 can monitor severalEPDCCH candidates or monitor for the enhanced control channel.Monitoring implies attempting to blindly decode one or more EPDCCHcandidates (in this example blind decoding can be attempted for each ofthe several EPDCCH candidates). It is noted that the DMRS required forEPDCCH decoding may be sent only when EPDCCH is sent, unlike the CRSwhich is sent always in every subframe even if PDCCH is not sent. EachEPDCCH candidate can be associated with a control channel element (CCE)or a set of aggregated CCEs. As used herein, in the context of theEPDCCH, these can be called enhanced control channel elements (eCCEs) todistinguish them from the CCE terminology used for PDCCH. Each enhancedcontrol channel element (eCCE) can comprise time-frequency resourceelements (REs) within the RBs of the EPDCCH RB set. The set of EPDCCHcandidates to be monitored by UE 106, that is, the EPDCCH candidate set,can also be defined in terms of search spaces. For example, an EPDCCHsearch space S_k_L at aggregation level L can refer to a set of EPDCCHcandidates where each candidate in the search space is has L aggregatedeCCEs. For PDCCH, aggregations of L=1, 2, 4, and 8 CCEs can besupported. For EPDCCH, the same aggregation levels may be supported.However, in another embodiment, since the size of eCCEs can be differentfrom the fixed CCE size of 36 REs, other aggregation levels (e.g. L=3)may be used. Also, since the size of the eCCEs can change considerablybetween different subframes and slots within a subframe (for example,based on legacy control region size or presence of CSI-RS, based onsubframe type), a set of aggregation levels that the UE 106 assumes forEPDCCH monitoring also may vary between subframes or between slots in asame subframe or between different subframe types (for example, a normalsubframe vs. an MBSFN subframe). More generally, a set of aggregationlevels that the UE assumes for EPDCCH monitoring can vary between afirst time period and a second time period. The EPDCCH candidates thatUE 106 monitors can be further divided into a set of common search spacecandidates (or enhanced common search space (eCSS) to differentiate withthe CSS for PDCCH), and a set of UE specific search space candidates (orenhanced UE specific search space (eUESS) to differentiate with the UESSfor PDCCH). eCSS candidates may be monitored on a EPDCCH RB set that isbroadcast to all the UEs in the coverage area of the serving eNB, thatis, eNB. For example, in LTE, this information can be broadcasted in aMaster Information block (MIB) or in a System Information Block (SIB).The eUESS candidates may be monitored on a EPDCCH RB set that issignaled to the UE via UE specific higher layer signaling.

Typically, the downlink control channel information can be a downlinkassignment or an uplink grant. A downlink assignment may include one ofmore of a downlink resource allocation information, DL HARQ information,DL MIMO information, power control commands, user identifier or RNTI,etc. Similarly, the UL grant may include uplink resource allocationinformation, uplink HARQ information, uplink MIMO information, powercontrol commands, user identifier or RNTI, etc. The DCI payload can beconvolutionally encoded, and then rate-matched and mapped to resourceelements based on the search space, where the number of resourceelements may be determined based on the aggregation level and CCE size(or eCCE size).

For ease of reference, the following abbreviations may have been used inthis disclosure:

RNTI Radio Network Temporary Identifier

HARQ Hybrid Automatic repeat request

MBSFN Multi-Media Broadcast over a Single Frequency Network

MIMO Multiple Input Multiple Output

T×D Transmit Diversity

DL Downlink

UL Uplink

CCE Control Channel Element

BLER Block Error Rate

PDCCH Physical Downlink Control Channel

OOS Out-of-Synchronization

IS In-Synchronization

eNB enhanced Node B

UE User Equipment

OFDM Orthogonal Frequency Division Multiplexing

RLF Radio Link Failure

RLM Radio Link Monitoring

HO Handover

CQI Channel Quality Information

CSI Channel State Information

CRS cell-specific reference signal

CSI-RS CSI-reference signal

DMRS Demodulation reference signal

QPSK Quadrature Phase Shift Keying

QAM Quadrature Amplitude Modulation

DCI Downlink Control Information

UCI Uplink Control Information

PDSCH Physical Downlink Shared Channel

CSS Common Search Space

UESS UE-specific Search Space

PMI Precoding Matrix Indicator

BGI Beamforming Gain Indicator

MAC Medium Access Control

RRC Radio Resource Configuration

SIB System Information Block

MIB Master Information Block

Embodiments within the scope of the present disclosure may also includecomputer-readable media for carrying or having computer-executableinstructions or data structures stored thereon. Such computer-readablemedia can be any available media that can be accessed by a generalpurpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to carryor store desired program code means in the form of computer-executableinstructions or data structures. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or combination thereof) to a computer, the computerproperly views the connection as a computer-readable medium. Thus, anysuch connection is properly termed a computer-readable medium.Combinations of the above should also be included within the scope ofthe computer-readable media.

Embodiments may also be practiced in distributed computing environmentswhere tasks are performed by local and remote processing devices thatare linked (either by hardwired links, wireless links, or by acombination thereof) through a communications network.

Computer-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Computer-executable instructions also includeprogram modules that are executed by computers in stand-alone or networkenvironments. Generally, program modules include routines, programs,objects, components, and data structures, etc. that perform particulartasks or implement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of the program code means for executing steps of the methodsdisclosed herein. The particular sequence of such executableinstructions or associated data structures represents examples ofcorresponding acts for implementing the functions described in suchsteps.

While the present disclosure and the best modes thereof have beendescribed in a manner establishing possession by the inventors andenabling those of ordinary skill to make and use the same, it will beunderstood that there are equivalents to the exemplary embodimentsdisclosed herein and that modifications and variations may be madethereto without departing from the scope and spirit of the disclosure,which are to be limited not by the exemplary embodiments but by theappended claims.

What is claimed is:
 1. A method in a user equipment of determining aradio link quality of a radio link, the method comprising: receiving afirst type of reference signal; monitoring, at the user equipment, for afirst type of control channel, the first type of control channeldemodulated based on the first type of reference signal; estimating afirst synchronization condition associated with the radio link based onthe first type of reference signal, the first synchronization conditionbeing one of a group comprising an out-of-synchronization condition andan in-synchronization condition; acquiring configuration informationrelated to configuration of a second type of control channel, the secondtype of control channel demodulated based on a second type of referencesignal, the second type of reference signal distinct from the first typeof reference signal; monitoring for the second type of control channel;estimating a second synchronization condition associated with the radiolink based on the second type of reference signal, the secondsynchronization condition being one of a group comprising anout-of-synchronization condition and an in-synchronization condition;and sending an output from a current layer to a higher layer based on atleast one of the estimated synchronization conditions, whereinestimating the second synchronization condition associated with theradio link is further based on energy per resource element informationrelating to enhanced physical downlink control channel transmission. 2.The method of claim 1, wherein estimating the second synchronizationcondition associated with the radio link is further based on at leastone of a set of configured virtual resource block set and a set ofconfigured subframe set.
 3. The method of claim 1, wherein estimatingthe second synchronization condition associated with the radio link isfurther based on antenna port set configuration for enhanced physicaldownlink control channel transmission.
 4. The method of claim 1, whereinsending an output further comprises transmitting an indicator to a basestation based on the output sent to the higher layer.
 5. The method ofclaim 1, wherein estimating the second synchronization conditionassociated with the radio link is further based on assuming at least oneof a hypothetical downlink assignment or an uplink grant.
 6. The methodof claim 1, wherein further assumptions for estimating the secondsynchronization condition are acquired via configuration signaling. 7.The method of claim 1, wherein, monitoring for a first type of controlchannel comprises monitoring at least one of a first common search spaceand a first user equipment search space.
 8. The method of claim 1,wherein monitoring for the second type of control channel furthercomprises monitoring at least one of a second common search space and asecond user equipment search space.
 9. The method of claim 1, whereinthe first type of control channel comprises a physical downlink controlchannel and the second type of control channel comprises an enhancedphysical downlink control channel.
 10. The method of claim 1, whereinthe first type of reference signal comprises a cell-specific referencesignal and wherein the second reference signal comprises a demodulationreference signal.
 11. The method of claim 1, wherein the first type ofreference signal comprises a cell-specific reference signal and whereinthe second reference signal comprises channel state informationreference signal.
 12. The method of claim 1, wherein the firstsynchronization condition comprises an out-of-synchronization conditionand wherein the second synchronization condition comprises anin-synchronization condition.
 13. The method of claim 1, furthercomprising determining an out-of-synchronization condition of the radiolink if the first synchronization condition is out-of-synchronizationand the second synchronization condition is out-of-synchronization. 14.The method of claim 1, wherein estimating the second synchronizationcondition associated with the radio link is further based on the firsttype of reference signal.
 15. The method claim 1, wherein the first typeof reference signal and the second type of reference signal are receivedon a first carrier.
 16. The method of claim 15, where the first type ofcontrol channel monitored spans the entire first carrier bandwidth andwhere the second type of control channel monitored spans only a portionof the first carrier bandwidth.
 17. The method of claim 1, where it isassumed that the first type of control channel monitored spans thebandwidth of a first carrier used for transmitting the first type ofcontrol channel and where it is assumed that the second type of controlchannel monitored spans only a portion of the bandwidth of a secondcarrier used for transmitting the second type of control channel.
 18. Auser equipment comprising: a transceiver; and a processor coupled to thetransceiver, the processor configured to receive a first type ofreference signal, the processor configured to monitor, at the userequipment, for a first type of control channel, the first controlchannel demodulated based on the first type of reference signal, theprocessor configured to estimate a first synchronization conditionassociated with the radio link based on the first type of referencesignal, the first synchronization condition being one of a groupcomprising an out-of-synchronization condition and an in-synchronizationcondition, the processor configured to acquire configuration informationrelated to configuration of a second type of control channel, the secondcontrol channel demodulated based on a second type of reference signal,the second reference signal distinct from the first type of referencesignal, the processor configured to monitor for the second type ofcontrol channel, the processor configured to estimate a secondsynchronization condition associated with the radio link based on asecond type of reference signal, the second synchronization conditionbeing one of a group comprising an out-of-synchronization condition andan in-synchronization condition, and the processor configured to send anoutput from a current layer to a higher layer based on at least one ofthe estimated synchronization conditions, wherein estimating the secondsynchronization condition associated with the radio link is furtherbased on energy per resource element information relating to enhancedphysical downlink control channel transmission.
 19. The user equipmentof claim 18, where the processor further sends an output by transmittingan indicator to a base station via the transceiver based on the outputsent to the higher layer.
 20. The user equipment of claim 18, whereinthe first type of control channel comprises a physical downlink controlchannel and the second type of control channel comprises an enhancedphysical downlink control channel.